Fusarium oligoseptatum sp. nov., a mycosymbiont of the ambrosia beetle Euwallacea validus in the Eastern U.S. and typification of F. ambrosium

Authors: AOKI, T - National Agriculture And Food Research Organization (NARO), Agricultrual Research Center; KASSON, M - West Virginia University; BERGER, M - West Virginia University; FREEMAN, S - Volcani Center (ARO); GEISER, D - Pennsylvania State University; O Donnell, Kerry

Submitted to: Fungal Systematics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2018
Publication Date: 2/19/2018
Citation: Aoki, T., Kasson, M.T., Berger, M.C., Freeman, S., Geiser, D.M., O'Donnell, K. 2018. Fusarium oligoseptatum sp. nov., a mycosymbiont of the ambrosia beetle Euwallacea validus in the Eastern U.S. and typification of F. ambrosium. Fungal Systematics and Evolution. 1(1):23-39. https://doi.org/10.3114/fuse.2018.01.03.
DOI: https://doi.org/10.3114/fuse.2018.01.03

Interpretive Summary: Invasive fungus-farming, wood-boring Euwallacea ambrosia beetles pose a growing threat to urban landscapes, forest ecosystems, and avocado production within the U.S. and worldwide. Five different Asian Euwallacea species are currently established within the U.S. Each Euwallacea species cultivates 1-2 different Fusarium species as a source of nutrition in galleries constructed by females in diverse woody hosts. Females have specialized mouth parts within which they transport their Fusarium symbiont in their natal galleries and from one woody host to another. This study was initiated to characterize the Fusarium symbiont that is cultivated by the invasive Asian ambrosia beetle Euwallacea validis in Ailanthus altissima (tree-of-heaven) symptomatic for wilt in south-central Pennsylvania. Formally described as F. oligoseptatum, this species can be distinguished by the unique club-shaped spores that it produces and by genetic analyses of DNA sequence data from portions of several genes. In addition, the Fusarium ambrosium symbiont of the Euwallacea ambrosia beetle that infests Chinese tea in India and Sri Lanka was characterized using molecular and morphological data to foster communication within the scientific community. Results of this study should be of interest to quarantine officials and diverse agricultural scientists who are charged with preventing the introduction and spread of these economically destructive pests both within and outside the U.S.

Technical Abstract: Fusarium oligoseptatum sp. nov. was isolated from the invasive Asian ambrosia beetle Euwallacea validis (Coleoptera, Scolytinae, Xyleborini) and from the galleries that females had constructed in dying Ailanthus altissima (tree-of-heaven) symptomatic for Verticillium wilt in south-central Pennsylvania, USA. This ambrosia fungus was cultivated by Euwallacea validis as the primary source of nutrition together with a second symbiont, Raffaelea subfusca. Female beetles transport their fungal symbionts within and from their natal galleries in paired pre-oral mycangia. Fusarium oligoseptatum was distinguished phenotypically from the 11 other known members of the Ambrosia Fusarium Clade (AFC) by uniquely producing mostly 1–2 septate clavate sporodochial conidia that were swollen apically. Phylogenetic analysis of multilocus DNA sequence data resolved F. oligoseptatum as a genealogically exclusive species-level lineage but evolutionary relationships with other members of the AFC were unresolved. Published studies have shown that F. oligoseptatum can be identified via phylogenetic analysis of multilocus DNA sequence data or a PCR multiplex assay employing species-specific oligonucleotide primers. In addition, to provide nomenclatural stability, an epitype was prepared from an authentic strain of F. ambrosium that was originally isolated from a gallery constructed in Chinese tea (Camellia sinensis) by E. fornicatus in India, together with its lectotypification based on a published illustration.